Monday, July 23, 2012

Over this past week I got the chance to do something that I haven't been able to much recently: Run QRP HF from the trail while backpacking. This trip was a 5-day backpack treck in the Wind River mountain range of Wyoming (near-ish Pinedale) with the vast majority of it being above 10,000 feet (3000 meter) elevation.

Unfortunately, I didn't get a chance to operate as much as I'd wished: There's something about being tired after carrying a 50+ lb (23kg) full-frame backpack full of everything you need to survive for 8 miles (over 12km) each day at such a high altitude that sometimes makes you want to just lay down for the evening rather than run around finding trees and rocks suitable for stringing an antenna!

As it turned out, only 2 QSOs were made on the trip - and at least some of this "minimalist" result was due to the fact that the HF bands seemed to be badly disturbed due to high solar activity: Only 40 meters seemed to be remotely usable during the times I could operate (approximately 6-8pm local time).

Figure 1:The ATS-3A (lower-left) and its band modules (top). In the lower-right is a modified Hendricks Altoids (tm) longwire tuner.Click on the image for a larger version.

The station was fairly simple: A Sprint ATS-3A (see an EHam review of this series of rigs here) running into a modified HendricksAltoids Longwire (end-fed) tuner and using about 60 feet (18 meters) of end-fed wire with a similarly-long counterpoise running in the opposite direction. The power source was a block of 8-10 AA cells (a mix of NiMH and a pair of "dead" alkaline cells from the GPS receiver) yielding a 9-13 volt DC source allowing the transmitter to produce between 2 and 4 watts.

As it turns out I could hear something on about every band that I tried (40, 30 and 20) but on all but 40 meters signals were extremely weak - even though I could hear an obvious difference in the background (atmospheric) noise on any band when I connected/disconnected my antenna! On the two occasions that I was able to get on the air, 40 meters sounded rather "odd" - very rapid fluttering and a "hollow" sound often associate with auroral disturbances.

Figure 2:The carrying bag with the entire multi-band HF station,sans power source and antenna wire. A "nerd knife"is shown for size comparison.Click on the image for a larger version.

In tuning around on 40 meters I heard more than one instance of the CW note of the station being received being "split" into two separate CW notes a few Hz or 10's of Hz apart: In many instances, the CW signals were so badly distorted that I wasn't able to make much sens of them - except during the brief periods when the distortion relented and the signal momentarily "cleaned up". It was in those instances that running, say, 7-10 WPM would have been required instead 15-18 WPM that I was hearing!

Perhaps the weakest link of the QRP station was the antenna. While I had a total of 120 feet of wire to spread out, it was rather difficult to find somewhere to sling that much wire, get it up a reasonable height into the air and still place it somewhere convenient to the operation station! Being that the entire station was to be as lightweight as possible (since I was carrying it!) I had to forgo things like coax, so the antenna and counterpoise wire pretty much had to end where the tuner and CW transceiver was located: Being that we were swarmed by bloodthirsty mosquitoes and deer flies it was most advantageous to operate from within the tent - yet another restriction on where our antenna wire could run!

For the most part the antenna consisted of the 60-ish feet of wire suspended only 6-16 feet (2-5 meters) above the ground since there never seemed to be conveniently-located cliffs nearby nor very tall trees just above our heads where we camped - which was pretty much at or above the tree line! The best we could do was to either sling the wire across a slight gully or run it up the hillside, paralleling the ground, and tie the far end to the rather short trees found at those altitudes.

As for the QRP gear itself, it worked pretty well: The Sprint ATS-3A (by Steve Weber, KD1JV) worked flawlessly - as did the tuner. Connected to the radio instead of earphones so that both of us (the other party being Brett, N7KG - whose callsign we used for one of the QSOs) could hear the audio was a modified Radio Shack amplified speaker. For CW keying I used my homebrew, lightweight portable paddles - easy enough to use at 12-15 WPM, but rather clumsy at speeds higher than this.

Figure 3:The environs of one of the night's QRP operations in the Wind River range of Wyoming.Click on the image for a larger version.

For power on the trip I brought along a folding 12 watt solar panel and with this I charged both camera and HT batteries and once those devices were charged I reconfigured things to top off the NiMH AA cells as appropriate. I'd started out with 10 fully-charged AA cells, but as my GPS receiver ran down a pair, these would be swapped into the 10-cell holder. For charging the depleted cells I would pop out the remaining fully-charged AA cells and jumper the empty positions with a clip lead to prevent their overcharging.

As it turned out the 12 watt folding panel was almost adequate for the needs: At best we had only 2-3 hours of sun when we arrived at camp in the evening and another hour or two of sun in the morning before departing, not leaving too much time to top everything off! Had I been out another 4-5 days, I'd have to have rationed power, but this situation could have been improved had I been able to devise some sort of "MPP" (Maximum Power Point) "switching" type charger for the panel rather than simple, inefficient brute-force charging which amounted to either dumping 12-15 volts into a linear 5-volt regulator for USB-type charging devices (my HT, for example) or simply shunting across the panel to top off the AA cells! Had I some sort of efficient energy conversion system I could have likely doubled my overall charging power efficiency!

Monday, July 9, 2012

Several years ago on "Astronomy Picture of the Day" I saw an article about Solargraphs - a topic that recurs ever year or so. Essentially, this is a long-exposure pinhole camera set outside on a (mostly) static scene.

The technology is quite simple:

Empty a soup can by eating its contents.

Empty an aluminum soda pop can by drinking its contents - or finding someone do that for you.

Get black-and-white print paper from wherever - preferably not panchromatic, but use what you can find.

Cut a 1cm (1/2") window in the soup can

Cut a 3-4cm (1-1/2-2") square piece out of the middle of the side of the soda pop can

Punch a small (0.5mm) hole in the middle of the above piece of the pop can. Try to make the hole as "clean" as possible.

Using black electrical tape, attach the piece of aluminum to the side of the soup can, centering the the pinhole over hole in the soup can. Make sure that the attachment point is light-proof, hence the use of black electrical tape - but don't cover the pinhole! (Duct Tape isn't necessarily light-proof so I'd avoid it.)

Fashion a lid for the top of the soup can. I've been able to take the rest of the flat aluminum side of the soda can and form it over the top of the soup can (careful of the sharp edges!) and make a lightproof "hat".

In subdued light - preferably dim red, say from a photographic safelight, an astronomer's flashlight or a red LED (if you used Orthographic paper) cut a piece of photo paper that is about the height of the inside of the soup can and will wrap most of the way around the inside.

Inside the can, place the paper, the emulsion side facing toward and centered on the pinhole.

Using black electrical tape again, tape the "hat" on top of the can to make it light-proof.

Gently put a piece of tape over the pinhole.

Photographic print paper is a bit harder to get locally than it used to
be: When I got my supply, I went to a local photo shop that I'd gone to
years ago to get my developing supplies and asked where they kept the
paper. Somewhat to my chagrin, I was directed to a single shelf
in a corner where there was a sparse assortment of miscellaneous, dusty
items. The only good part about this experience was that everything on
this shelf - including the three remaining packs of photo paper - where
on sale and heavily discounted. The paper itself was more than a year
out of date, but that's really not much of a concern for black and white
paper stored at reasonable temperatures and is even less important when
used in a solargraph! (On the web, it's very easy to find photographic print paper for cheap, so don't despair if you can't get it locally.)

Figure 1:
A solargraph - pointed mostly south - at my workplace.Click on the image for a larger version.

You now have a rudimentary pinhole camera. Place it outside or in a window, attached to something solid that will not move (avoid a tree, if possible as it sways and bows with wind and season). I attach it using nylon wire ties to a post, but one could duct-tape it - but make sure that it is solid and will NOT shift! It is also best to place it such that it will not be directly exposed to rain and snow - a wooden or metal "hat" attached just above it on a pole or fence post outside would be good and don't forget to remove the piece of tape placed over the pinhole during assembly!

Now, leave it alone for several months, taking good notes on where, exactly, you left it if you happen to be placing it out of the way - say, in the woods.

It is recommended that one orients the pinhole of the solargraph such that it faces toward the sun (e.g. south for those in the northern hemisphere) but a view toward the east or west is also good. If you live way north or south (arctic/antarctic circle) then it might be interesting to point it north (or south)-ish during the summer-ish months.

Results of some of these solargraphs may be seen in the attached images. The above is the first solargraph that I'd done, taken by attaching a soup-can camera to a metal railing at my work in a location with a south-facing view showing the thick arc of the sun as it changed its elevation over several months in the year. In the images are ghostly vestiges of snow and vehicles that were intermittently present during its exposure.

When I did my first solargraph I didn't know what to expect and upon removing the paper (again, in subdued, red light) the image was a bit faint, so I did what anyone would do: I immersed the photo print paper in some warm coffee to develop it* - and develop it did, much more quickly than I'd expected! Before I knew it, the paper had turned a very warm brown from being overdeveloped and not just from the coffee!

At this point, the image was negative, of course, so I placed it on the photo scanner and digitized it, protecting it from light beforehand: After scanning I noticed that the paper was even darker (and of lower contrast) than before so it's best to NOT scan it more than absolutely necessary since you are, in fact, "burning" away the image by doing so!

Figure 2:
Winter/Spring exposure looking southwest from a location in the
mountains central Utah at about 8400ft (2560m) elevation.Click on the image for a larger version.

Once digitized it's easy to invert the image and as if by magic, there's a semblance of the original scene - and, amazingly enough, in color - on black-and-white print paper!

I'm not sure exactly how the color part works, and to be sure, it really doesn't work very well so the pictures on this page have been somewhat color and contrast-enhanced using GIMP, a free image manipulation program, but I'm sure that you'll agree that the results are tantalizing, if not amazing!

The second solargraph was taken over a much longer period of time (5 months) and placed at a remote cabin in central Utah, attached to a support on a deck. From the track of the sun one can clearly see the apparent motion of its track from the winter solstice to well into spring - a month or so shy of the summer solstice. On the ground for much of this time was snow, but it being white its image remained even though the ground was at least partially bare for the last month or so of the picture.

With its longer and more complete exposure - and now knowing what to expect - I removed the paper from the soup can camera and placed it directly into the scanner (again, in subdued light) and after inverting and a bit of brightness/contrast/color tweaking, got the picture you can see and with the more thorough exposure, the result was much better than the first attempt. The scene itself lacks color, but that's generally true of winter!

Again, one of the most fascinating aspects of this is that negative pseudo-color images result with the use of black-and-white photographic print paper - and without the need for any developing at all! It's also interesting to see the changing path of the sun over a period of months - and even of cloudy days as evidenced by the breaks in the yellow sun tracks!

* As it turns out, some of the constituents of coffee act to develop photographic film and paper - not particularly well, as it turns out, but it does work and is described on a lot of web sites.

Monday, July 2, 2012

These days, finding a frequency to expand ones repeater system can be a challenge - even in "rural" parts of the country such as Utah where the Salt Lake area is about the only large population center for hundreds of miles.

Figure 1:
The Scott's Hill site, part of the UARC 146.620 systemClick on the image for a larger version.

Typically, a linked repeater system consists of several repeaters tied together on a backbone frequency and each of these individual repeaters is usually on its very own frequency: About the only time that frequency re-use is implemented is if several of these individual repeaters are located far enough apart that they won't bother each other and it is often the case that different subaudible tones are used to prevent mutual interference should a user be in an area with potential overlap.

More than a decade ago the Utah Amateur Radio Club decided to expand the coverage of its 146.620 repeater and a mountaintop site was secured - a story in and of itself to be told another day, perhaps. As things often happen the project lay fallow for several years until a set of circumstances provided the ambition and impetus to push it along farther.

From the beginning, the intent was to have a "Synchronous" and "Voting" repeater on this other site, Scott's Hill, that was to share the same frequency as the original repeater on Farnsworth Peak, but putting together such a system was understandably more involved than the typical linked (but each site using a different frequency) repeater system.

The original repeater on Farnsworth Peak provides impressive coverage, from north of the Utah/Idaho border, west beyond the Utah/Nevada border, to the south into parts of central Utah but pretty much stopping at the Wasatch range to the east of the Salt Lake metro area. For the most part, the coverage of Salt Lake area repeaters is limited eastward by the abrupt rise of an 11,000 foot mountain range along the east side of the populated areas and unless a repeater is located atop those mountains, coverage to the east is minimal. Unfortunately - or fortunately - repeaters located in the Wasatch intended to provide coverage to the high valley areas east of the Salt Lake Valley tend not to provide good coverage into the Salt Lake valley itself owing to the shielding effects of the mountains themselves - that is, the taller peaks on which repeaters are placed are generally set back a bit and the somewhat lower "front" peaks to their west tend to block the view of the valley.

Scott's Hill is such a site: It sees well from the East through the Northwest but it can actually see none of the Salt Lake valley to the south and west. It does, however, have a good, line-of-sight view of Farnworth Peak, so the linking between the two sites is pretty easy. This general exclusivity of coverage also means that having the two repeaters effectively sharing the same frequency would be simplified as there were relatively few places where the two would overlap with comparable signal levels.

Figure 2:
Voting controller for the 146.620 system.Click on the image for a larger version.

Now, how does one go about putting two repeaters on the air, on the same frequency, without their clobbering each other?

Multiple receivers on the same frequency:

For receive, the answer is pretty easy: Voting receivers.

On a "Voting" system, one typically brings the audio from all of the separate receivers to one central location and there, they are all analyzed for signal quality and the best of the lot is selected and used as the audio source for the entire system.

Compared to the typical linked system where the user selects which repeater/frequency is to be used, there are advantages to having ONE frequency with multiple (voting) receivers:

Easier to use. If there is only ONE frequency, the users don't have to constantly change to the best frequency for the area from which they are transmitting - assuming that they know which is the best for their specific location!

Frequency re-use. With a voting system, only ONE frequency is required which can save a bit of spectrum.

The whole is greater than sum of the parts. On a multi-receiver system, it's typical that while one particular receiver works best for a specific area, it's also likely that the less-optimal receivers will also provide a degree of coverage in that same area. If one enters an area where coverage is a bit "spotty" on the primary-coverage receiver, there's a reasonable chance that one of the other receivers may be able to still hear the mobile and "fill in" - all of this without the user having to worry about it!

The addition of even more receivers. Once the "base" voting system is installed, it's practical to install additional "fill" receivers for those areas where better coverage might be desired: These extra receivers need only be a simple receiver and link transmitter rather than a full-blown repeater requiring a lot of expensive filters.

While there are a number of ways that voting systems can work, pretty much all of them exploiting a "feature" of the frequency modulation (FM) that we use on our VHF and UHF bands: Quieting.

You have probably noticed that as an FM signal sounds the same whether it is very strong or weak - at least until the signal gets to be really weak - at which point it starts to sound noisy but NOT quieter! If one were to listen carefully, it might also be observed that the noise tends to start out at the higher frequencies first - and this is how a radio's squelch works: It listens for the high-pitched hiss that starts to show up as the signal gets weak.

Most voters listen for this "hiss." On a typical system, since all of the receivers are listening to the same audio being transmitted, the one with the least amount of hiss is, in fact, the one receiving the best signal. If you think about it, all one really needs to determine is which one has the least amount of "audio plus hiss" as the only thing that will be different among the receivers with different-quality signals will be the amount of hiss on them.

Ideally, one would do this comparison at the receiver itself where one has access to the "guts" of the receiver and can look at the "discriminator audio" where the spectral content can go into the 10's of kHz. Practically speaking, however, we have to link these individual receivers back to one site for the voting and conventional FM link radios can't pass the 10's of kHz of audio necessary to do this so the "audio plus hiss" scheme is used. The voter on the 146.620 system works this way, mostly looking at the higher-frequency audio (e.g. above 2.5-3 kHz) to determine which of the inputs has the "best" signal (e.g. least "audio plus hiss.")

There are other ways to do this - including digital means where precise signal quality measurements are telemetered to the main controller - but our intent was to construct the entire system using "off the shelf" radio modules that were available on the surplus market so that there would be a reasonable hope of it being maintained in the future.

This article - including more details on two transmitters sharing the same frequency - continues in Part Two.